This invention relates to a centrifugal pump wheel of that type which is generally comprised of a centrifugal pump wheel having at least one covering plate or disk, a plurality of pump wheel vanes and gas evacuation openings located leeward of respective vanes of the pump wheel, as well as to a method of pumping a liquid which contains gas and possibly also solids, particularly paper pulp, by means of a centrifugal pump.
It is known in the art that centrifugal pumps get substantially deteriorated performance characteristics when the pumping of liquids containing free gases is concerned. In pumping of gas containing water the pump can operate with a gas content of about 10-15%, however with substantially less satisfactory performance characteristics than at the pumping of clean water. This is evident from the diagram in FIG. 1.
In some suspensions which beside gas contain solids, such as paper pulp, the pump action ceases completely at an air content of about 5%, as is evident from the diagram in FIG. 2.
To improve the performing characteristics of pumps intended for the pumping of paper pulp and the like one has therefore evacuated gases from the pump fluid through an aperture or a conduit behind the pump wheel. To make this evacuation of gas more effective the pump wheel additionally has been provided with holes. In the belief that primarily the heavier mixture of liquid and solids would be thrown radially outwards in the direction towards the circumference of the pump wheel by the centrifugal force, whereas the gas would be collected more centrally, the major part of these gas evacuation openings has hitherto always been located adjacent the centre of the pump wheel.